Direct Evidence that Cholesterol Ester Hydrolase from Adrenal Cortex is the Same Enzyme as Hormone‐Sensitive Lipase from Adipose Tissue

Abstract

Several properties of the cytosolic cholesterol ester hydrolase from bovine adrenal cortex were investigated and those properties were compared directly with those of the well-characterised hormone-sensitive lipase, the ratelimiting enzyme in adipose tissue lipolysis. Properties examined included : (a) activity against different substrates; (b) susceptibility to inhibition by NaF, Hg2+ ions and diisopropyl fluorophosphonate; (c) subunit molecular weight as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate ; (d) ability to serve as a substrate for cyclic AMP-dependent protein kinase; (e) effect of phosphorylation on enzyme activity: and (f) degradation pattern of polypeptides following limited proteolysis.In all respects the two enzymes exhibited essentially identical characteristics. It is therefore concluded that the same protein, or two very similar proteins, catalyses the hydrolysis of cholesterol esters in adrenal cortex and lipolysis in adipose tissue.The implication of this finding is discussed in relation to the hormonal control of steroidogenesis in adrenal cortex and of lipolysis in adipose tissue.Cholesterol ester hydrolase catalyses one of the ratelimiting steps in steroidogenesis in the adrenal cortex [I]. This enzyme catalyses the release of free cholesterol from stores of cholesterol esters present as lipid droplets in the cytoplasm. The free cholesterol is then transported into the mitochondria where it is converted to pregnenolone by the side-chain cleavage enzyme system. Following stress induced by ether anaesthesia, which is known to elevate the circulating levels of corticotrophin, the cholesterol ester stores are depleted and the activity of the cholesterol ester hydrolase is elevated [2]. Corticotrophin is thought to exert most of its effects via the actions of cyclic AMP, and it has been shown that, in the high-speed supernatant from adrenal cortex, the cholesterol ester hydrolase becomes activated following incubation with cyclic AMP and Mg-ATP [3], suggesting that activation results from phosphorylation of the enzyme.In addition to cholesterol esters, the lipid droplets contain significant levels of phospholipids and triacylglycerol, and adrenal cortex contains a triacylglycerol hydrolase which also becomes activated in response to corticotrophin [4]. This has led to the suggestion that one enzyme may catalyse both the cholesterol ester and triacylglycerol hydrolase activities and indeed the two activities co-purify through a limited purification procedure [ 5 ] . The ratio of the two activities does vary, however, in fractions obtained by precipitation at different concentrations of ammonium sulphate and the cholesterol ester hydrolase is more susceptible to inhibition by active Ahhrc.~'icrrions. DFP, diisopropylfluorophosphonate; corticotrophin, adrenocorticotrophic hormone; QAE-Sephadex, quaternary diethylL(2-hydroxypropy1)aminoethyl-Sephadex.En=~w?e.s. Cholesterol esterase or cholesterol ester hydrolase (EC 3.1.1.13): triacylglycerol lipase or...

Localization of hormone‐sensitive lipase to rat Sertoli cells and its expression in developing and degenerating testes

“…The previously proposed function of HSL in steroidogenic tissues is the mobilization of free cholesterol for steroid biosynthesis [4,32,34,37]. However, the lack of expression of HSL in Leydig cells demonstrated in this study, together with the apparent lack of steroid hormone synthesis from cholesterol in Sertoli cells [38], seriously question this proposal, at least with regard to testis.…”

“…These stores are thought to be important for steroid biosynthesis and spermatogenesis [1][2][3][4][5]. Spermatogenesis is severely impaired by temperature elevation, and we have previously shown that experimental cryptorchidism in the rat leads to a decrease in testicular cholesterol esterase activity, concomitant with increased lipid accumulation in Sertoli cells [6,7].…”

Metabolomic analysis of adrenal lipids during hypoxia in the neonatal rat: implications in steroidogenesis

“…Hormone-sensitive lipase (HSL) present in the adrenal also acts as a cholesterol esterase, and lack of HSL activity significantly decreases ACTH-stimulated corticosterone production (7,18). HSL activity is modulated through hormonal/neuronal mechanisms (e.g., free fatty acid release from adipocytes).…”

Phosphorylation of bovine hormone‐sensitive lipase by the AMP‐activated protein kinase

“…The AMP-activated protein kinase would thus not only exert a feedback regulation of the synthesis of fatty acids (via phosphorylation of acetyl-CoA carboxylase) but also of their release from triglycerides. HSL has been shown to act as a hormone-sensitive, cholesterol-ester hydrolase in steroidogenic tissues, controlling the release of free cholesterol from intracellular stores of cholesterol esters [21,221. The AMP-activated protein kinase may therefore regulate both the synthesis of cholesterol (via phosphorylation of 3-hydroxy-3-methylglutaryl-CoA reductase) and its release from intracellular stores.…”